This invention relates to an orthodontic screw-type biassing device, and more particularly to such a device including means for preventing the screws from being disengaged from their threaded receptacles.
Screw-type orthodontic devices have been known for many years, one such typical device being illustrated in U.S. Pat. No. 3,832,778 to M. Wallshein. Recently, multi-screw devices, using nested screw arrangements, have been developed, such as those disclosed in U.S. Pat. No. 4,107,843 and in U.S. application Ser. No. 785,587, filed Apr. 7, 1977 by Mr. Wallshein. The entire contents of U.S. Pat. No. 4,107,843 and of U.S. patent application Ser. No. 785,587 are incorporated herein by reference. A problem in the art of designing and fabricating screw-type actuators for orthodontic biassing elements is to prevent the screws from being disengaged from their respective threaded receptables. In the multi-screw arrangement of U.S. Pat. No. 4,107,843, a shoulder-stop arrangement is provided to prevent the larger screw from coming out of its body housing, but there is no means provided for preventing the smaller screw from becoming disengaged from the larger screw. Patent application Ser. No. 785,587 shows various different constructions for preventing disengagement of the screws, both the large screws and the small screws, from their respective threaded receptacles to prevent inadvertent disassembly of the device in the mouth.
The object of this invention is to provide a simplified and easy to manufacture construction for preventing threaded screws from becoming disengaged from their threaded receptacles.